The present disclosure relates to image sensors, and in particular, to CMOS image sensors.
An image sensor is a semiconductor device that converts optical images into electrical signals. Image sensor may be classified into one of two types: a charge coupled device (CCD) type and a complementary metal-oxide-semiconductor (CMOS) type. A CMOS-type image sensor (CIS) may include a plurality of two-dimensionally arranged pixels, each of which includes a photodiode (PD) that coverts incident light into an electrical signal.
As the integration density of image sensors increases, the size of each pixel or photodiode in the image sensor becomes smaller and smaller. This may lead to a reduction in the amount of light incident into each photodiode and a consequent deterioration in the sensitivity of the image sensor.